This invention relates to electrostatographic reproduction machines that include original document illuminating means and transparent platens for holding original documents being illuminated for reproduction. More particularly, the present invention relates to such an electrostatographic reproduction machine having a cover that enables cooling of its transparent glass platen.
In conventional light lens or scanner type electrostatographic reproduction machines, an original document to be reproduced is manually placed or automatically conveyed onto a glass platen. The original document on the platen is illuminated by an elongate lamp assembly located in an optics cavity, either by moving the platen while the lamp is held stationary, or by moving the lamp assembly beneath a stationary platen. Alternatively, both the scan lamp and the platen can be held fixed and the document moved across the platen surface in a continuous velocity transport (CVT) mode.
In any of these cases, a problem to be anticipated is a buildup of heat at the platen from operation of the document illuminating lamps. The lamps used for document scanning, for example, are typically mercury fluorescent or tungsten halogen lamps. With either source, but particularly with the tungsten halogen type of lamp, the heat buildup at the platen can become a source of concern. For example, with continued usage, such a platen may become so hot as to present a safety concern for the machine operator or cause defects in the glass platen.
Various approaches therefore have been devised and disclosed, for example, in the following patents for glass platen cooling in electrostatographic reproduction machines.
U.S. Pat. No. 4,945,383 discloses an image forming apparatus which includes a temperature control device to control the temperature of light on a photosensitive medium. The apparatus is comprised of a pair of cooling fans and a heat ray reflecting shutter. The heat ray reflecting shutter aids in the ventilation created by the fans.
U.S. Pat. No. 4,632,539 discloses an apparatus for cooling a fluorescent lamp by causing a flow of cooling air to pass along a conduit extending along the length of the lamp.
U.S. Pat. No. 5,136,328 discloses a contoured scanning lamp reflector which entrains air flow underneath a platen glass and around the scanning lamp assembly for disturbing a boundary layer of heat thereof and cooling the lamp and platen.
Unfortunately, however, such conventional airflow devices which are located underneath the glass platen, are only partially effective because much of the heat from the document illuminating lamps reaches the glass platen through empty space as radiation. Radiant heat as such will pass through moving air which appear transparent to heat waves in the infrared range. Therefore, despite the use of air flow devices underneath the glass platen. The glass platen still builds up heat, particularly during long copy runs of a single original document when the cover of the machine is stationary and down over the document. The stationary cover which, in the clown position, serves to conform the document to the platen, traps heat over the platen, thus further heating the platen and raising its temperature.